Leigh (1951) described an infant who developed somnolence, hearing loss, optic atrophy, and signs of pyramidal tract involvement and the baby died 6 weeks later. Autopsy revealed subacute necrotizing encephalomyelitis, involving the brainstem, thalamus, basal ganglia, and the posterior column of the spinal cord. After similar cases have been added to the literature, this condition is called Leigh encephalopathy, Leigh syndrome, or subacute necrotizing encephalopathy in infants. Later delayed abnormalities in the mitochondrial function owing to mitochondrial mtDNA and nuclear DNA dysfunction was discovered in this condition. Approximately 60 contributory mutations have been reported including those showing of maternal, AR or XR inheritance patterns. Among these, the common mutations are those occurring in the mtDNA MTATP6 gene and the nuclear gene PDHA1 that encodes the pyruvate dehydrogenase complex (Naito, 2002).
Myopathological findings are usually non-specific and include fibers with low COX activity. RRFs are usually absent. Some patients show no histopathological changes. Documentation of changes in the basal ganglia and thalamus on head MRI is important to establish a diagnosis.